Synthesis of alpha-haloacrylonitrile

ABSTRACT

A METHOD OF PREPARING A-HALOACRYLONITRILES FROM A,A,BTRIHALOPROPIONITRILES COMPRISING THE STEP OF ADDING A DEHALOGENATING AGENT SELECTED FROM THE GROUP OF A TRIALKYL PHOSPHITE AND A TRIHYDROCARBYLPHOSPHINE AT A TEMPERATURE OF FROM 0-60*C.

United States Patent M 3,659,006 SYNTHESIS OF a-HALOACRYLONITRILE Kailash C. Pande, Parkershurg, W. Va., assignor to Borg- Warner Corporation, Chicago, Ill. No Drawing. Filed June 17, 1969, Ser. No. 834,151 Int. Cl. C07c 121/30 US. Cl. 260465.7 1 Claim ABSTRACT OF THE DISCLOSURE A method of preparing a-haloacrylonitriles from uc,ot, 3- trihalopropionitriles comprising the step of adding a dehalogenating agent selected from the group of a trialkyl phosphite and a trihydrocarbylphosphine at a temperature of from 0-60 C.

BACKGROUND OF INVENTION Prior to the instant invention, a great many methods were provided for the production of unsaturated aliphatic halonitriles, perhaps the most prevalent method of preparing monohaloacrylonitrile was by the dehydrohalogenation of saturated halogenated (chlorinated or brominated) nitriles containing 3 to 8 carbon atoms in the mole cule. One of the primary difficulties of dehydrohalogenation prior to this invention was the requirement of high temperatures and relatively uneconomical catalysts with particularly complex reactions that resulted in relatively uneconomical processes. Also, many of the previous reactions provided a series of halogenated compounds which were somewhat difficult to separate to obtain the desired end product.

An example of prior art methods of preparing u-haloacrylonitrile from dechlorination of 0c,zx,fltl'lChlOI0pI0- pionitrile is set forth in US. Pat. 2,384,889 wherein the dehalogenation is conducted at temperatures between 100 200 C., in addition to the high temperature used, the yields are relatively low, i.e., in the order of 40%. In this specific dehalogenation method, a magnesium complex is used and the dehalogenation is carried out in the presence of a solid.

SUMMARY OF INVENTION The instant invention is directed to the preparation of a-haloacrylonitrile by the dehalogenation of a,u,/3-trihalo propionitrile. The a, fl-trihalopropionitrile is prepared by bubbling a halogen such as fluorine, bromine or chlorine through acrylonitrile at a proximately room temperature. Under normal room temperature conditions, an excellent yield of trihalopropionitrile is obtained. The dehalogenation of the a,a,B-trihalopropionitrile is conducted by adding a trialkyl phosphite (OR) P with R equal to an alkyl group containing from 1 to 10 carbon atoms or trihydrocarbylphosphine (R) P with R selected from the group C -C alkyl and C C aryl. The reaction with trialkyl phosphite takes place at a temperature of ()60 C. and the conversion is almost quantitative following the reaction sequence.

EQUATION I wherein R is an alkyl group containing 1-10 carbon atoms and X is fluorine, chlorine or bromine.

3,659,006 Patented Apr. 25, 1972 The process set forth in the equation may be further modified to m,B-brominated, chlorinated propionitrile using the following equations:

The reaction of this invention will be more clearly understood in view of the following examples wherein all parts are by weight unless otherwise indicated.

Example 1 52.5 g. a,a,B-trichloropropionitrile was charged to a three-necked flask equipped with a magnetic stirrer, condenser and a dropping funnel. 50 g. of triethyl phosphite was added to the flask in a dropwise manner. An exothermic reaction occurred and the temperature was held between 5-35 C. by external cooling. After addition of the phosphite, the reaction was maintained at room temperature for an additional half-hour. The majority of the ethyl chloride was evaporated OlT and the mixture was heated. About 3 g. of a low boiling fraction (33 C.) was collected. After the low boiling fraction was discarded, the main fraction contained in excess of u-ChlOIO- acrylonitrile (about 26.5 g. with a yield of about 98%). The a-chloroacrylonitrile had a B.P. 83-95 C. Prolonged fractionation of the mixture at reduced pressure yielded 0,0-diethylchlorophosphate (26.6 g. having a B.P. of 50/ 1 mm. Hg). The u-chloroacrylonitrile was further characterized by its retention time in VPC, IR and NMR spectra.

Example 2 The reaction conditions of Example 1 were repeated and instead of adding triethyl phosphite, 1 mole of trimethyl phosphite was added to a,a,,8-trichloropropioni trile at 10-25 C. ot-chloroacrylonitrile in a yield of about 90% wasobtained.

Example 3 Using the reaction conditions of Example 1, 12 g. of trimethyl phosphite was added dropwise to 30 g. of ot,oz,13- tribromopropionitrile. The temperature rose from 2545 C. and after complete addition of the phosphite, the reaction mixture was kept at 50 C. for an additional onehalf hour. Fractionation of the reaction mixture yielded 70% of a-brornoacrylonitrile with the B.P. of 5253/ 85 mm. The product wasv further identified by IR and NMR spectra.

. Example 4 Using the reaction conditions of Example 1, 13 g. of triethyl phosphite was added to- 32 g. of a,;8-dibromo-achloropropionitrile. The temperature was maintained between 20 C. and 40 C. After the complete addition of the phosphite, the reaction mixture was fractionated to yield a-chloroacrylonitrile (85% yield, B.P. 82-85 0.).

Example 5 Using the reaction conditions set forth in Example 1, 30 g. of a,a,B-tribromopropionitrile and a-fiuoro-u,5-dibromopropionitrile in the ratio of 60:40'was placed in a reaction flask. 15 g. of trirnethyl phosphite was added to the flask and after complete addition, the reactant mixture was kept at 45 C. for 15 minutes. The fraction yielded a-fluoroacrylonitrile (3.0 g.) with a B.P. of 39- 42 C. and of u-bromoacrylonitrile (7.5 g.) B.P. 56-59 C./ 98 mm.

Example 6 Team. ether solution of a,e43-trichloropropionitrile (26.0 g. in 75 ml. of ether) was added an ether solution of triphenylphosphine (16.0 g. in 100 ml. ether). An exothermic reaction occurred, immediate precipitate of triphenylphosphorus dichloride was formed. This was filtered, the. filtrate on analysis on VPC gave about 60% yield of a-chloroacrylonitrile.

4 Example 7' To an ether solution of a,afi-trichloropropionitrile (26.0 g. in 75 ml. of ether) was added an ether solution of tri-n-butylphosphine (25.0 g.). An exothermic reac tion occurred and an immediate precipitate formed. After filtration, the filtrate was fractionated giving about yield of u-chloroacrylonitrile.

The aforementioned examples have illustrated the preparation of oi-haloacrylonitrile through the dehalogenation of a,e,,8-trihalopropionitrile. It will be understood that the invention has been described in connection with certain specific embodiments thereof and this is by way of illustration only and not by Way of limitation and that the scope of the invention is defined solely by the ap- 060 C. References Cited UNITED STATES PATENTS 2,385,550 9/1945 Spence 260-465.7 3,361,786 1/1968 Fink 260--465.7 3,527,787 9/1970 Baader et al. 260-4659 JOSEPH P. BRUST, Primary Examiner US. or. X.R. 

